The endothelial-cell-derived secreted factor Egfl7 regulates vascular tube formation

Abstract

Vascular development is a complex but orderly process that is tightly regulated. A number of secreted factors produced by surrounding cells regulate endothelial cell (EC) differentiation, proliferation, migration and coalescence into cord-like structures. Vascular cords then undergo tubulogenesis to form vessels with a central lumen. But little is known about how tubulogenesis is regulated in vivo. Here we report the identification and characterization of a new EC-derived secreted factor, EGF-like domain 7 (Egfl7). Egfl7 is expressed at high levels in the vasculature associated with tissue proliferation, and is downregulated in most of the mature vessels in normal adult tissues. Loss of Egfl7 function in zebrafish embryos specifically blocks vascular tubulogenesis. We uncover a dynamic process during which gradual separation and proper spatial arrangement of the angioblasts allow subsequent assembly of vascular tubes. This process fails to take place in Egfl7 knockdown embryos, leading to the failure of vascular tube formation. Our study defines a regulator that controls a specific and important step in vasculogenesis.

c-MYC overexpression with loss of Ink4a/Arf transforms bone marrow stromal cells into osteosarcoma accompanied by loss of adipogenesis

“…Of the 24 000 genes examined, we focused on those that contribute to differentiation or development (Table 1). Key genes for the regulation of embryonic organogenesis (Hoxa5, Hoxa9, Foxc1 and Foxf2) and the commitment of immature cells to multiple lineages (Pparg, Cebpa, Plxnd1, Egfl7, Mgp, Plxdc2, Ebf1 and Tcf3) were expressed at higher levels in AO cells than in AX cells, suggesting that AO cells have characteristics of immature mesenchymal cells (Wang and Reed, 1993;Luo et al, 1997;Wu et al, 1999;Rosen et al, 2000;Parker et al, 2004;Torres-Vazquez et al, 2004;Miller et al, 2007;Cole et al, 2008). The profile of AX cells, on the other hand, was indicative of both cells that are committed to the osteocyte lineage (Dlx3, Sp7, Dkk1, Ostn and Bmp3) and cells that are inclined to tumorigenesis in vivo (Cd276, Ptgs2, Vegfa, Epha2, Frzb and Sfrp1) (Kim et al, 1993;Daluiski et al, 2001;Dannenberg et al, 2001;Thomas et al, 2003;Lee et al, 2004 Zang et al, 2007;Brantley-Sieders et al, 2008;Engin et al, 2008;Li et al, 2008).…”

Egfl7 knockdown causes defects in the extension and junctional arrangements of endothelial cells during zebrafish vasculogenesis

“…In our previous studies, we performed Egfl7 gene knockdown (KD) in zebrafish. Silencing of Egfl7, which is normally expressed from the seven-somite stage onward, had no significant influence on the proliferation and long distance migration of endothelial progenitors during formation of the midline angioblasts, the stage that precedes vascular tube formation in the trunk of the embryo (Parker et al, 2004). Analysis by confocal microscopy showed that the DA and PCV were formed in the correct location, from normal numbers of ECs and with the correct expression of several tested EC markers.…”

“…One of the key factors that play a role in the regulation of vascular development is EGFL7 (also called VEstatin; Soncin et al, 2003), a secreted protein with an evolutionarily conserved structure and expression pat-tern from fish to human (Fitch et al, 2004;Parker et al, 2004). Egfl7 is expressed exclusively in ECs and their progenitors.…”

“…The expression level is high during embryonic and neonatal development, but low in most adult blood vessels. After secretion, EGFL7 remains associated with the extracellular matrix at the basal side of the endothelial lining of blood vessels (Parker et al, 2004). In our previous studies, we performed Egfl7 gene knockdown (KD) in zebrafish.…”

“…However, the segregation of arterial and venous EC cords and lumen formation were severely impaired. In addition, extensive tight junctions were retained in the solid EC cords instead of being refined during tubulogenesis (Parker et al, 2004). Accompanying defects in the embryos were an incomplete circulatory loop, pericardial edema, and hemorrhages (Parker et al, 2004).…”